The present invention relates to an injection pump and, more particularly, to an fuel injection pump electro-mechanically controlling the fuel injection rate and injection timing.
The supply of fuel into an internal combustion engine at a high pressure has been made by a fuel injection pump. Recently, there is an increasing demand for an electronic control of the fuel injection pump, in which the rate and the timing of fuel injection are controlled. Such apparatus is disclosed in U.S. Pat. No. 4,185,779 issued on Jan. 29, 1980.
The conventional fuel injection pumps of the kind described incorporate servo mechanisms of various types and the controls for the fuel injection rate and timing are achieved by a feedback control of the servo mechanism.
In the fuel injection pumps in which the fuel injection rate is controlled, the fuel is charged by a solenoid valve into a high-pressure chamber in which the fuel is pressurized to a high pressure, and the amount of fuel injection per stroke of the plunger is determined by the timing of opening of the solenoid valve.
In the fuel injection pumps incorporating the servo mechanisms, the servo mechanisms are usually of the electric-hydraulic type servo mechanisms using the fuel itself as the medium. In fuel injection pumps of this type, the servo mechanism is too complicated and expensive, as is the electromechanical control circuit. In addition, the relationship between the mechanical position of the servo mechanism and the injection rate or timing, initially obtained after the assembling of the pump, is gradually changed as the mechanism is used a long time, due to wear or the like reason.
In the fuel injection pumps in which the injection rate is controlled through the control of opening timing of the solenoid valve, no consideration is made as to the control of the injection timing. If this type of injection pump is required to have a function for controlling also the fuel injection rate, it is necessary to combine this pump with the servo mechanism of the same type as that used in the first-mentioned type of fuel injection pump. Such a combination, however, is accompanied by the same problems as stated before.